This invention relates to an electro-optical device applied as an image display device to drive an electro-optical material layer by making use of plasma, thus to carry out selection of pixels.
As the means for allowing, e.g., a liquid crystal display to have high resolution and high contrast, there is generally carried out a method in which active elements such as transistors, etc. are provided every display pixels to drive them (which method is so called an active matrix addressing system).
In this case, however, since it is necessary to provide a large number of semiconductor elements such as thin film transistors, the problem of yield is apprehended particularly when the display area is enlarged, giving rise to the great problem that the cost is necessarily increased.
Thus, as the means for solving this, Buzaku et al. have proposed in the Japanese Laid Open Application No. 217396/89 publication a method utilizing discharge plasma in place of semiconductor elements such as MOS transistors or thin film transistors, etc. as an active element.
The configuration of an image display device for driving a liquid crystal by making use of discharge plasma will be briefly described.
In this image display device, as shown in FIG. 7, a liquid crystal layer 101 serving as an electro-optical material layer and plasma chambers 102 are adjacently arranged through a thin dielectric sheet 103 comprised of glass, etc.
The plasma chambers 102 are constituted by forming a plurality of grooves 105 in parallel to each other in a glass substrate or base plate 104. Within these chambers, ionizable gas is filled. Further, pairs of electrodes 106 and 107 in parallel to each other are provided at respective grooves 105. These electrodes 106 and 107 function as an anode and a cathode for ionizing gas within the plasma chambers 102 to generate discharge plasma.
For example, the electrodes 106 function as an anode, and are commonly wired and grounded. Further, the electrodes 107 function as a cathode, and are connected to transistors through current limiting resistors.
On the other hand, the liquid crystal layer 101 is held by the dielectric sheet 103 and a transparent substrate 108. On the surface at the liquid crystal layer 101 side of the transparent substrate 108, transparent electrodes 109 are formed. These transparent electrodes 109 are perpendicular to the plasma chambers constituted by the grooves 105. The portions where the transparent electrodes 109 and the plasma chambers 102 intersect with each other correspond to respective pixels.
In the above-mentioned image display device, pulse voltages are applied in sequence to electrodes 107 serving as the cathode by ON/OFF of the transistors, whereby discharge plasma takes place in a time series manner by discharge between the electrodes 106 and 107 in respective plasma chambers 102. Then, by switching and scanning in sequence the plasma chambers 102 where plasma discharge is carried out by ON/OFF of the transistors, and applying signal voltages to the transparent electrodes 109 on the liquid crystal layer 101 side in synchronism with the switching scan operation, these signal voltages are held by respective pixels. The liquid crystal layer 101 is thus driven.
Accordingly, the grooves 105, i.e., plasma chambers 102 respectively correspond to one scanning lines, and two kinds of electrodes of an anode and a cathode are required every scanning unit.
Meanwhile, since image display devices of this kind carry out the operation as an optical shutter in the state where these electrodes 106 and 107 are included in the display region as well, in the case where the electrodes 106 and 107 are formed by, e.g., opaque material such as metal, light at these portions is absorbed or reflected. This is an obstacle to an effective operation as an optical shutter. In actual terms, the above-mentioned image display devices involve the great problem that existence of these electrodes 106 and 107 lowers transmissivity or transmission factor, thus degrading brightness of the image display device.
Accordingly, it is desirable to adopt a method of forming these electrodes 106 and 107 by a transparent material, or a method of narrowing the stripe width, etc. thereby holding down lowering of the transmissivity to a minimum level.
However, because there actually exists occurrence of sputter phenomenon followed by plasma discharge, a metal film such as Ni, etc. must be used as an electrode material.
Further, it is obvious that the method of narrowing the stripe width of the electrodes 106 and 107 has a limit particularly in the case of forming a high resolution and high density pattern in order to avoid occurrence of defects due to breakage at the time of manufacturing or at the time of operation.
As stated above, in the conventional image display devices, improvement in transmissivity and requirement of high resolution are contrary to each other.